Reduced cost of reactive power in doubly fed induction generator wind turbine system with optimized grid filter

The modern grid requirement has caused that the wind power system behaves more like conventional rotating generators and it is able to support certain amount of the reactive power. For a typical doubly-fed induction generator wind turbine system, the reactive power can be supported either through the rotor-side converter or the grid-side converter. This paper firstly compares the current ripples and supportive reactive power ranges between the conventional L and optimized LCL filter, if the reactive power is injected from the grid-side converter. Then, the loss distribution is evaluated both for the generator and the wind power converter in terms of the reactive power done by the rotor-side converter or the grid-side converter with various grid filters. Afterwards, the annual energy loss is also estimated based on yearly wind profile. Finally, experimental results of the loss distribution are performed in a down-scaled DFIG system. It is concluded that over-excited reactive power injected from the grid-side converter has lower energy loss per year compared to the over-excited reactive power covered by the rotor-side converter. Furthermore, it is also found that the annual energy loss could even become lower with the optimized filter and thereby more energy production for the wind turbine.